Trying to build an LED Driver which will run with Vehicle Battery

[MSMorkan]

Hello Everyone,

I am trying to drive LEDs which requires 2.9V forward voltage and 1A current.

Currently circuits have 4 LEDs in series and have various of channels. I can change the LEDs to 3 in series if needed but channel will be increased as well.

4LEDs x 4 (4 AMPS), 4LEDs x 8(8AMPS) and 4LEDs x 16(16AMPS). I need to build a common PCB for all of them but components on them may vary.

Now, I use Meanwell LDD-1000L 1A constant current for each channel (Vin must be higher than Vout). It costs too much (3.6-4$ for each LDD-1000L) and also I cannot fit them in the case. I need to design my own 1A (for each channel) constant current power supply. But I am stuck at choosing the right integrated device.

This is the case for 12V vehicle battery which has a voltage around 12-14.5V

For 24V vehicle battery: I convert 8LEDs in series and reduce channel to half by soldering 0 ohm resistors to my PCB. In this case I use half of constant current sources but still cost is too much and still occupies a lot of space.

I am open to any advices about replacing LDD-1000L with custom design PCB.

My first thought is using a 1.5A DC-DC buck converter circuit + current limiting resistor for each channel.
Also I have another question for this one. What happens if I connect 2 or more parallel DC-DC buck convertors and draw 2 or more ampers from them instead of using higher current rated DC-DC buck converter? Is it harmful for short/long-term usage?

Thanks a lot
Have a nice day
and Sorry for my bad English :-(
>M.Suat

 

[KlausST]

Hi,

It's not clear to me how many LEDs you want to connect... 16? 32? 64? Any other count?

For the battery:
* expect voltage range of 10.5V .... 14.4V for 12V nominal lead acid battery.
* or 21V ... 29V for a 24V battery.

Consider either step down
* less than 10.5V output voltage for a 12V system
* less than 21V output voltage for a 24V system

Or a step up system
* more than 14.4V for a 12V system...

Klaus

 

[summitville]

He is saying, the current design is 4 LED'S in series per string at 1 amp

Then ...
4 strings = 4 amps
8 strings = 8 amps
16 strings = 16 amps

The design can be changed from 4 LED's in series per string, to 3 LED's in series per string, to allow more overhead voltage.
But then 33% more "3 LED" strings are needed to keep the same total number of LED's in the overall design.

4 LED's per string x 2.9 v per LED = 11.6 Volts per string
3 LED's per string x 2.9 v per LED = 8.7 Volts per string

Yes, you can parallel Constant Current Sources to provide the total amps needed for the exact number of string attached = 4, 8 or 16 strings.

The LM317 is very small and cheap ( $0.50 each ) CC supply - use one per 4 LED series string?
It can supply 1 amp given a small ( Vin - Vout ) voltage difference = keep watts dissipated low and attach to metal.
LM317 is a Linear supply = not very efficient unless controlled / constant small Voltage Differential
The problem with a Car Battery is ... the voltage can vary from 12 Volts to 14.4 volts !
Use a CV Buck-Boost Inverter ( at rated amps ) in front of the array of LM317's ?

If your battery is only 10.5 Volts either ...
a) the car engine is cranking or
b) the battery is dead
In either case, your LED's should not be ON.

 

[KlausST]

Hi,

He is saying,

I know what he is saying...

But where do I find the information how many LEDs in total the OP wants to control...

Klaus

 

[MSMorkan]

Hi,


I know what he is saying...

But where do I find the information how many LEDs in total the OP wants to control...

Klaus

Thanks for reply,

Number of LEDs varying between 16 and 64. So we can assume that it will be multiple of 16 LEDs.

@summitville
Thanks for suggestions,
LM317 sounds inefficient. Average voltage difference will be around 2V. Each string will have a power loss of 2W + serial resistor will cause a power loss (Will there be a serial resistor with this solution?)
That is why I need DC-DC buck/boost converter with a serial resistor (1 to 5 ohm). Do you agree with this?

So the final question is:
Should I use DC-DC buck/boost converter or LM317?

If DC-DC buck/boost which component(s) or integrated circuit(s) should I use?

Thank you very much

Suat

Edit:

Someone suggested me this circuit:
https://www.electroschematics.com/9383/led-constant-current/
What do you think?

 

[treez]

you sometimes have vout = 2.9v
sometimes vout is 12v
Your vin is 10 to 14v
So if i was you i would use a buckboost or coupled sepic